Investigating the electronic portal imaging device for small radiation field measurements

Agarwal, Arpita; Rastogi, Nikhil; Das, KJ Maria; Yoganathan, SA; Udayakumar, Durga; Kumar, Shaleen

doi:10.4103/jmp.jmp_131_16

Cited by 10 publications

(8 citation statements)

References 40 publications

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“…Additionally, EPIDs over-respond to low-energy photons, 49 and have a dose rate dependence. 50 Studies with EPIDs have shown 16-23% errors in output factors for small field size (~8 mm 2 x 8 mm 2 ) in one study 51 and ~8% difference to film for measurements of small target plans (~3 mm 2 x 3 mm 2 ) in another. 50 Without appropriate correction of these dependencies, 4,52 errors may be present.…”

Section: Introductionmentioning

confidence: 98%

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

et al. 2020

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The SRS MapCHECK â , a recently developed patient-specific quality assurance (PSQA) tool for end-to-end testing of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT), was evaluated in a multi-institution study and compared with radiochromic film. Methods: The SRS MapCHECK was used to collect data on 84 SBRT or SRS PSQA plans/fields at nine institutions on treatment delivery devices (TDD) manufactured by Varian and Elekta. PSQA plans from five different treatment planning software (TPS) were selected and executed on TDDs operating at beam energies of 6 and 10 MV with and without a flattening filter. The patient plans were all VMAT except for ten conformal arc therapy fields. The plans were selected to encompass a range of size and tumor sites including brain, lung, spine, abdomen, ear, pancreas, and liver. Corresponding radiochromic film data was acquired in 50 plans/fields. Results were evaluated using gamma analysis with absolute dose criterion of 3% global dose-difference (DD) and 1 mm distanceto-agreement (DTA). Results: The mean 3% DD/1 mm DTA Gamma pass rate of SRS MapCHECK in comparison to film was 95.9%, whereas comparison of SRS MapCHECK to the treatment planning software was 94.7%. 80% of SRS MapCHECK comparisons against film exceed 95% pass rate, and about 30% of SRS MapCHECK comparisons against film exceed 99% pass rate. To maintain good agreement between SRS MapCHECK and film or TPS, authors recommend avoiding plans with a modified modulation complexity score (MMCS) <0.1 arbitrary units (a.u.). In the examples presented, this coincides with avoiding plans with a mu/dose limit of >3 µ/cGy. Conclusions: Stereotactic radiosurgery MapCHECK has been validated for PSQA for a variety of clinical SRS/SBRT plans in a wide range of treatment delivery conditions. The SRS MapCHECK comparison with film demonstrates near-equivalence for analysis of patient-specific QA deliveries comprised of small field measurements.

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Section: Introductionmentioning

confidence: 98%

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

et al. 2020

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“…EPID based dosimetry was recently investigated for small field sizes (down to 2x2cm 2 ) using a conventional linac [84] . Other groups have implemented portal dosimetry for VMAT SBRT treatments [85] , [86] .…”

Section: Phantom-less Methods For Dosimetry Auditsmentioning

confidence: 99%

Novel methodologies for dosimetry audits: Adapting to advanced radiotherapy techniques

Pasler¹,

Hernández

Jornet

et al. 2018

Physics and Imaging in Radiation Oncology

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With new radiotherapy techniques, treatment delivery is becoming more complex and accordingly, these treatment techniques require dosimetry audits to test advanced aspects of the delivery to ensure best practice and safe patient treatment. This review of novel methodologies for dosimetry audits for advanced radiotherapy techniques includes recent developments and future techniques to be applied in dosimetry audits. Phantom-based methods (i.e. phantom-detector combinations) including independent audit equipment and local measurement equipment as well as phantom-less methods (i.e. portal dosimetry, transmission detectors and log files) are presented and discussed. Methodologies for both conventional linear accelerator (linacs) and new types of delivery units, i.e. Tomotherapy, stereotactic devices and MR-linacs, are reviewed. Novel dosimetry audit techniques such as portal dosimetry or log file evaluation have the potential to allow parallel auditing (i.e. performing an audit at multiple institutions at the same time), automation of data analysis and evaluation of multiple steps of the radiotherapy treatment chain. These methods could also significantly reduce the time needed for audit and increase the information gained. However, to maximise the potential, further development and harmonisation of dosimetry audit techniques are required before these novel methodologies can be applied.

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“…22,[30][31][32][33][34][35] In recent years, the use of the electronic portal imaging device (EPID) for pre-treatment patient-specific treatment plan verification has gained increased interest due to its simplicity. 22,23,[26][27][28][29][35][36][37][38][39] The Varian EPID has been shown to be capable of producing high-resolution measured dose digital images which can be compared with predicted portal dose images calculated by the Eclipse TM Treatment Planning System (TPS) based on the actual fluence distribution for every patient treatment plan fields. 22,23,[28][29][30]36,40,41 Various methods including the dose difference (DD), distance-to-agreement (DTA) and the gamma (γ) index have been used to compare the measured and predicted dose images.…”

Section: Introductionmentioning

confidence: 99%

“…22,23,[28][29][30]36,40,41 Various methods including the dose difference (DD), distance-to-agreement (DTA) and the gamma (γ) index have been used to compare the measured and predicted dose images. [22][23][24][26][27][28][29][30][35][36][37][38][39][42][43][44] The DD is the difference in dose at a specified point in each of the predicted and measured dose distributions, and it is reflected as a percentage of the maximum dose, whereas the DTA represents the nearest distance between two points of equal dose on the predicted and measured dose images when superimposed. 22,23,30,42,43,45 According to Low et al 42 and Low & Dempsey, 43 the DD method is very sensitive in areas of high-dose gradient and a small spatial misalignment will cause a large DD between the measured and the calculated dose distributions, whereas the DTA method is sensitive in areas of low-dose gradient and a small DD in low-dose area could result in large DTA values.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, it is a common practice to compare the predicted and measured dose distributions using the gamma (γ) index technique which takes both the DD and DTA into consideration. [22][23][24][26][27][28][29][30][35][36][37][38][39][42][43][44] This evaluation method indicates a satisfactory agreement between a specific dose point in the predicted and measured dose images when the dimensionless quantity γ is ≤1, otherwise the dose point is considered to fail. 22,24,30,42,43 The overall agreement of a set of predicted and measured dose distributions is characterised by the percentage of dose points that fulfil passing criteria, known as the gamma passing rate (%GP).…”

Section: Introductionmentioning

confidence: 99%

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Retrospective analysis of portal dosimetry pre-treatment quality assurance of intracranial SRS/SRT VMAT treatment plans

2021

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Background: The complexity associated with the treatment planning and delivery of stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) volumetric modulated arc therapy (VMAT) plans which employs continuous dynamic modulation of dose rate, field aperture and gantry speed necessitates diligent pre-treatment patient-specific quality assurance (QA). Numerous techniques for pre-treatment VMAT treatment plans QA are currently available with the aid of several different devices including the electronic portal imager (EPID). Although several studies have provided recommendations for gamma criteria for VMAT pre-treatment QA, there are no specifics for SRS/SRT VMAT QA. Thus, we conducted a study to evaluate intracranial SRS/SRT VMAT QA to determine clinical action levels for gamma criteria based on the institutional estimated means and standard deviations. Materials and methods: We conducted a retrospective analysis of 118 EPID patient-specific pre-treatment QA dosimetric measurements of 47 brain SRS/SRT VMAT treatment plans using the integrated Varian solution (RapidArcTM planning, EPID and Portal dosimetry system) for planning, delivery and EPID QA analysis. We evaluated the maximum gamma (γmax), average gamma (γave) and percentage gamma passing rate (%GP) for different distance-to-agreement/dose difference (DTA/DD) criteria and low-dose thresholds. Results: The gamma index analysis shows that for patient-specific SRS/SRT VMAT QA with the portal dosimetry, the mean %GP is ≥98% for 2–3 mm/1–3% and Field+0%, +5% and +10% low-dose thresholds. When applying stricter spatial criteria of 1 mm, the mean %GP is >90% for DD of 2–3% and ≥88% for DD of 1%. The mean γmax ranges: 1·32 ± 1·33–2·63 ± 2·35 for 3 mm/1–3%, 1·57 ± 1·36–2·87 ± 2·29 for 2 mm/1–3% and 2·36 ± 1·83–3·58 ± 2·23 for 1 mm/1–3%. Similarly the mean γave ranges: 0·16 ± 0·06–0·19 ± 0·07 for 3 mm/1–3%, 0·21 ± 0·08–0·27 ± 0·10 for 2 mm/1–3% and 0·34 ± 0·14–0·49 ± 0·17 for 1 mm/1–3%. The mean γmax and mean γave increase with increased DTA and increased DD for all low-dose thresholds. Conclusions: The establishment of gamma criteria local action levels for SRS/SRT VMAT pre-treatment QA based on institutional resources is imperative as a useful tool for standardising the evaluation of EPID-based patient-specific SRS/SRT VMAT QA. Our data suggest that for intracranial SRS/SRT VMAT QA measured with the EPID, a stricter gamma criterion of 1 mm/2% or 1 mm/3% with ≥90% %GP could be used while still maintaining an in-control QA process with no extra burden on resources and time constraints.

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Investigating the electronic portal imaging device for small radiation field measurements

Cited by 10 publications

References 40 publications

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

Novel methodologies for dosimetry audits: Adapting to advanced radiotherapy techniques

Retrospective analysis of portal dosimetry pre-treatment quality assurance of intracranial SRS/SRT VMAT treatment plans

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